Representation of (x-7) and (x+1)

In summary, the diagram represents the inequality (x-7)(x+1) ≤ 0. The top row shows where x-7 is negative and positive, while the second row shows where x+1 is negative and positive. The product is positive for x>7 and x<-1, and negative for -1<x<7. This is because the product is positive when both factors are negative or positive, and negative when one factor is negative and the other is positive. It is important to understand the logic behind equations before using them, and the concept of dividing by zero does not apply to cross multiplication.
  • #1
#neutrino
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Mod note: Changed the title and this post to reflect the situtation in the diagram
the representation of the inequality (x-7)(x+1) ≤ 0 makes no sense to me . can someone explain this .
the diagram is attached
 

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  • #2
a times b < 0 if either a or b is negative and the other factor is positive. So they look at that. The vertical lines may be somewhat confusing to you ? The one with the 7 applies to x-7, which changes sign at x =7 and the one with the -1 applies to x = -1.
Both lines apply to the product, that changes sign both at x = -1 and at x = 7. From the +++ and the - - - you can conclude the sign of the product.
 
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  • #3
The top row shows where x- 7 is negative and positive- it is negative for all x< 7, positive for all x> 7.
The second row shows where x- 1 is negative and positive- it is negative for all x< 1, positive for all x> 1.

Since the product of two negative or of two positive number is positive while the product of one negative and one positive number is negative, the diagram shows that the product (x- 7)(x- 1) is positive for x< 1, where both factors, (x- 7) and (x- 1), are negative, positive for x> 7where both factors, (x- 7) and (x- 1), are positive, and negative for 1< x< 7 where (x- 7) is negative and (x- 1) is positive.
 
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  • #4
HallsofIvy said:
The top row shows where x- 7 is negative and positive- it is negative for all x< 7, positive for all x> 7.
The second row shows where x- 1 is negative and positive- it is negative for all x< 1, positive for all x> 1.

Since the product of two negative or of two positive number is positive while the product of one negative and one positive number is negative, the diagram shows that the product (x- 7)(x- 1) is positive for x< 1, where both factors, (x- 7) and (x- 1), are negative, positive for x> 7where both factors, (x- 7) and (x- 1), are positive, and negative for 1< x< 7 where (x- 7) is negative and (x- 1) is positive.
got it Thank you !
 
  • #5
#neutrino said:
the representation of the inequality (x-7)(x-1) ≤ 0 makes no sense to me . can someone explain this .
the diagram is attached
The formula in the diagram is (x-7)(x+1).

Mod note: edited the thread title and post #1 to reflect what's shown in the diagram.
 
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  • #6
correct ,sorry
 
  • #7
A simple way is that x should be such that product is negative or zero. hence x should be such that only one of two multiples is negative. If number is greater than 7 product will surely be positive and less than -1 both will be negative. I always tell try to understand logically the equations and understanding of euclid's axiom is highly required before using them. Some often gets confused that 0/0 is 1 as 1*0 is 0 and by cross multiplication...
There's nothing true in cross multiplication we divide both sides by zero and it gives 0/0 is 0/0. Sorry I got away from topic but I thought it would help and makes maths interesting and fun.
 

What is the representation of (x-7)?

The representation of (x-7) is an algebraic expression that represents the difference between x and 7. It can also be written as x minus 7 or 7 less than x.

What is the representation of (x+1)?

The representation of (x+1) is an algebraic expression that represents the sum of x and 1. It can also be written as x plus 1 or 1 more than x.

How do you solve equations involving (x-7) and (x+1)?

To solve equations involving (x-7) and (x+1), you can use the distributive property to expand and combine like terms. Then, isolate the variable on one side of the equation and solve for its value.

What is the graphical representation of (x-7) and (x+1)?

The graphical representation of (x-7) and (x+1) are two parallel lines on a Cartesian coordinate system with a slope of 1. The line for (x+1) is shifted 7 units to the left compared to the line for (x-7).

How are (x-7) and (x+1) related?

(x-7) and (x+1) are related as algebraic expressions that represent the difference and sum, respectively, between x and a constant value. They are also related as two parallel lines on a graph with a slope of 1 and a horizontal distance of 7 units between them.

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